This invention relates to an electronic device using a functional thin film such as a pyroelectric IR sensor and, more particularly, to an electronic device using a functional thin film wherein its electrode material is improved.
For example, Japanese Patent Laid-Open Publication No. 143258/1989 describes pyroelectric sensors wherein a pyroelectric element plate is formed from PbTiO.sub.3, Al or Pt is used as its lower electrode and NiCr is used as an upper electrode which acts also as an infrared absorption layer. Besides the foregoing, it also is known that Sn doped In.sub.2 O.sub.3 (ITO) be used as a lower electrode and that Al or gold black be used as an upper electrode.
When the metal or ITO is used as electrodes in the prior art, the following disadvantages occur in connection with the functional materials such as PbTiO.sub.3.
(i) The crystal structure of PbTiO.sub.3 and the like is fundamentally different from that of the metals and the like and therefore it is difficult to carry out epitaxial growth in forming PbTiO.sub.3 and the like by a thin film technique such as a laser ablation method.
(ii) The coefficient of thermal expansion of PbTiO.sub.3 and the like is greatly different from that of the metals and the like and therefore cracks and lattice defects are liable to occur due to the thermal stress during the film-forming process.
(iii) The metal electrode formed by the laser ablation method has an inferior surface, the metal electrode can have defects such as pinholes and such drawbacks are reasons why sensors having defects are produced.
(iv) The metals and the like have a high thermal conductivity, and therefore an incident energy cannot be effectively transformed into output charge in applying them to a pyroelectric IR sensor.
(v) The metals and the like have small emissivity (thermal absorption coefficient) and therefore it is disadvantageous to use the metals and the like as the upper electrode (light-receptive portion) of the pyroelectric IR sensor from the standpoint of efficiency.
An object of the present invention is to provide an electronic device using a functional thin film by which the above drawbacks (i) through (v) of the prior art can be solved.